High strength lithopone



Oct. 27, 1936.

L. S. HOLSTEIN HIGH STRENGTH LITHOPONE Filed Jumel 22, 1954 ATTORNEYSpone manufacture.

Patented Oct. 27, 1936 UNITED STATES PATENT OFFICE HIGH STRENGTHLITHOPON E Application June Z2, 1934, Serial No. 731,821

12 Claims.

This invention relates to high strength lithopone, and has for itsob-ject an improved method of making such lithopone. High strengthlithopone contains more than 30% Zinc sulphide, which is the approximatepercentage of Zinc sulphide in normal lithopone produced by the usualreaction of barium sulphide liquor with zinc sulphate solution asrepresented by the following equation:

vBaS-i-ZIlSOi: ZnS -i-BELSOL;

One of the heretofore customary methods of producing high strengthlithopone involves mixing, in predetermined proportions, crude normallithopone (coprecipitated zinc sulphide and barium sulphate) andseparately prepared Zinc sulphide, and subjecting the resulting mixtureto the customary subsequent operations of litho- In using crude washedZinc sulphide precipitated from a zinc sulphate solution by hydrogen4sulphide for producing high strength lithopone by that method, it hasbeen found that the nish'ed product is deficient in pigmentaryproperties in proportion to its Zinc sulphide content. I have discoveredthat this deficiency is due, in part at least, to the fact that the twodifferent types of zinc sulphide (namely, that in lithopone precipitatedby barium sulphide and that precipitated by hydrogen sulphide) requiredifferent muiiling or calcining treatments in order to bring out themost effective pigmentary properties. I have further discovered that thetwo different types of zinc sulphide may for all practical purposes bemade equally amenable to the same calcining `treatment by subjecting thezinc sulphide in lithopone to conditions of preparation similar to theconditions of preparation of the zinc sulphide precipitated by hydrogensulphide.

Based on these discoveries, myl invention contemplates the production ofhigh strength lithopone (containing over 30% zinc sulphide) by includingcrude coprecipitated Zinc sulphide and barium sulphate (crude normallithopone) in an aqueous slurry in which precipitation of zinc sulphideby the action between hydrogen sulphide and zinc sulphate is proceeding,and thereby subjecting the zinc sulphide in the coprecipitate to thesame conditioning environment as the zinc sulphide precipitated byhydrogen sulphide. 'Ihe crude coprecipitated zinc sulphide and bariumsulphate may be introduced into the slurry during any stage in theprecipitation of the zinc sulphide by hydrogen sulphide, or may beprecipitated in situ simultaneously with the Zinc sulphide by the jointaction of hydrogen sulphide and barium sulphide upon an aqueous solutionof zinc sulphate. The resulting precipitate mixture (i. e.coprecipitated zinc sulprecipitatedL by hydrogen sulphide) is Washed toremove acids and then subjected to the customary subsequent operationsof lithopone manufacture.

A characteristic feature of the invention is the exposure of crudecoprecipitated zinc sulphide and barium sulphate to the action of aslurry of crude Zinc sulphide in which the precipitation of zincsulphide by reaction with hydrogen sulphide gas is proceeding. Theresulting precipitate mixture, after Washing to remove acid andsubjection to the usual subsequent operations of lithopone manufacture,becomes a high strength lithopone having pigmentary properties superiorto those of the pigment produced by mixing crude lithopone withseparately prepared and washed crude zinc sulphide precipitated by thehydrogen sulphide process. It is my present belief that by the method ofthe invention the zinc sulphide in the crude coprecipitate is subjectedto a conditioning treatment similar to that given the zinc sulphideprecipitated by hydrogen sulphide and in consequence thereof the Zincsulphide in the coprecipitate has substantially the same properties asthe zinc sulphide precipitated by hydrogen sulphide. Thus, the resultingslurry of crude coprecipitate and crude zinc sulphide is homogeneouswith respect to the entire zinc sulphide content thereof so that thecalcining, quenching and finishing operations bring out the optimumtinting strength of both types of zinc sulphide.

In practicing the invention, it is not necessary that all of the crudenormal lithopone be exposed to the slurry in which the precipitation ofzinc sulphide by the action of hydrogen sulphide is proceeding. Thus, acrude high strength lithopone slurry containing 75% zinc sulphide may beproduced in accordance With the invention, and this crude slurry maythen be mixed in any appropriate manner with sufficient crude normallithopone to bring the zinc sulphide content down to between 50 and 60%.The resulting precipitate mixture, when calcined, quenched and finishedin the customary manner of litho-- pone manufacture, produces a highstrength lithopone of satisfactory pigmentary properties.

The precipitation of the Zinc sulphide by hydrogen sulphide ispreferably carried out in the manner disclosed in the copendingapplication for Letters Patent of the United States of Arne J. Myhrenand Byron Marquis, Serial No. 702,578, liled December l5, 1933, nowPatent No. 2,020,325. In that method the slurry, resulting from thepartial interaction oi hydrogen sulphide and Zinc sulphate, isrepeatedly mixed with hydrogen sulphide gas in a series of eductorsthrough which the gas is entrained by the slurry. In accordance With mypresent invention, coprecipitated Zinc sulphide and barium sulphate isincluded in this slurry at some appropriate stage during theprecipitation of Zinc sulphide by hydrogen sulphide. Thus, for example,the coprecipitate may be formed in situ in the slurry by introducingbarium sulphide liquor, or a crude slurry of normal lithophone may beintroduced into the slurry of Zinc sulphide being precipitated byhydrogen sulphide. Again, crude normal lithopone may be added to theZinc sulphide slurry during an aging treatment of several hours durationin the course of which substantial completion of the reaction betweenhydrogen sulphide and zinc sulphate takes place.

The invention will be more readily understood from the followingdescription taken in conjunction with the accompanying drawing, in whichthe single figure is a diagrammatic elevation of a suitable apparatusfor practicing the invention.

The apparatus illustrated in the drawing comprises three tanks 5, 5', 5(arranged in series), of circular cross-section and with conicalbottoms, each tank being provided with two Venturi tube eductors B and1, 6' and 'I' and 6" and l", respectively. The series of tanks isprovided with a gas inlet pipe 8" (entering the top portion of tank 5")and a gas outlet pipe 9 (discharging from tank 5). Gas pipes 8' and Bconnect the top portions of tank 5" and 5 and the top portions of tanks5 and 5, respectively. The system of pipes 8", 8', 8 and 9 connects thetanks in series at points above the normal level (a) of liquid or slurrytherein in such fashion that gas can flow freely through the series oftanks.

The gas outlet pipe 9 dips below the liquid-level (b) in a water sealI0. The gas space above the liquid-level (b) in the water seal I0 isconnected by a pipe II with the suction side of a fan I2. The pressureside of the fan I2 is connected by a pipe I3 with a screen-box I4, whichcontains metal screens set across the path of the gases therethrough.The screen box I4 is connected by a pipe I5 to a gas burner I6, providedwith a stack II.

The tanks 5, 5' and 5" are provided with pumps for liquid and/or slurrytransport, and pipe lines for liquid or slurry are appropriatelyconnected with the pumps, tanks and Venturi tube eductors in suchfashion that liquid and/or slurry can be transported through the seriesof tanks and likewise partly recirculated in the individual tanks, whilebeing brought into intimate contact with gas traversing the series oftanks in general counter-current with the liquid and/or slurry. Each ofthe six Venturi tube eductors (6, 1, 6', 1', E" and 1) is arranged torecirculate gas through the tank with which it is operativelyassociated, withdrawing gas through pipes 29, I9, 29', I9', 29", I9,respectively, wh-ile intimately mixing the gas with the liquid and/orslurry. The Venturi tube eductor 6 introduces the liquid into the systemby discharging it into tank 5. The Venturi tube eductors l, 'I' and I"serve to recirculate liquid or slurry through the tanks with which theyare connected (through tanks 5, 5 and 5", respectively) The Venturi tubeeductors 6' and 6 serve to convey liquid or slurry from one tank intothe next tank in the series. Thus, Venturi tube eductor 6 serves toconvey liquid or slurry (withdrawn from tank 5) into tank 5'; andVenturi tube eductor 6" serves to convey liquid or slurry (withdrawnfrom tank 5') into tank 5".

The apparatus shown in the drawing is similar to that shown anddescribed in U. S. Appl. Ser. No. 702,578 and is operated as follows forproducing a slurry of high strength lithopone in accordance with thepresent invention:

Hydrogen sulphide is introduced into the series of tanks through theinlet 8", and is drawn through tank 5", pipe 8', tank 5', pipe 8, tank5, outlet pipe 9 and water seal I0 by the suction produced by the fanI2. The effective suction of the fan I 2 is adjusted and regulated bysuitable adjustment of the water-level (b) in the water-seal ID;lowering of the water level b ini creasing the effective suction of thefan and raising of the water level decreasing the effective suction. Itwill be understood that the absorption of hydrogen sulphide by solutionin, and reaction with, the Zinc sulphate solution likewise tends to drawgas into the system through the pipe 8" by suction. The water-sealprevents air from entering the system when the fan I2 is shut down forany reason, as for example for the purpose of attaching a spare fan tothe gas outlet line 9.

The fan I2 forces the gas through the line I3, the screen box I4 and theline I5 to the gas burner I6. The products of combustion (e. g. sulphurdioxide) are removed from the burner I6 by the stack I`I. Back-ring offlame from the burner I6 into the system is guarded against by metalscreens (preferably made of a metal of high heat conductivity, e. g.copper) placed in the path of the gases in screen-box I4. The watersealI0 is a further safe guard against backfiring.

Purified zinc sulphate solution is introduced (preferably continuously)into the system by pump 20, which delivers the solution to the Venturitubereductor 6 through a pipe 2|. The amount of solution transported bythe pump 20 through the pipe 2l is regulated by adjustment of a pinchvalve 23 on a hose segment 22. The rate of flow of solution into theVenturi tube eductor 6 is indicated by a pressure gauge 24', connectedin the pipe line 2I at a point between the Venturi tube eductor 5 andthe pinch valve 23.

In passing through the Venturi tube eductor 6, the solution drawshydrogen sulphide gas from the tank 5 through the pipe 29 and thesolution and entrained gas are discharged into the tank 5. The gas isbrought into intimate contact with the solution in the form of thinfilms and small droplets in the eductor so that the reaction betweenhydrogen sulphide and Zinc sulphate is initiated, with the formation ofa slurry of zinc sulphide, zinc sulphate and sulphur-ic acid.

The Venturi tube eductor is preferably so operated as to entrain withthe solution a volume of gas greatly in excess of the volume ofsolution; for example, the volume of hydrogen sulphide gas carriedthrough the eductor by the solution may be from 25 to 50 times thevolume of the solution, or even more.

The slurry charged into the tank 5 through the eductor 6 is withdrawnfrom the orifice in the conical bottom of the tank through the pipe 32by the pump 3l, which forces the slurry through the pipe 33, into thebranch pipes 34 and 2I. The relative amounts of slurry flowing intothese branch pipes are regulated by appropriate adjustments of pinchvalves 35 and 23 on hose segments 35 and 22', respectively. Pressuregauges 3'I and 24', respectively, indicate the prevailing pressures andthus the rates of flow in these two branch pipes. The slurry enteringthe Venturi tube eductor I is mixed therein with hydrogen sulphide gastaken from the tank 5 through the pipe I9, and then returned to tank 5.The eductor l functions with respect to mixing the gas (taken from thetank 5 through the pipe 29) and slurry in the same manner as the eductor6. The slurry entering the branch pipe 2i passes into the eductor 6',which iunctions in the same manner as eductor 5, with respect to mixingthe slurry with gas (except, oi course, that the eductor 6 draws gasthrough its gas-pipe 29 from the tank 5'). The eductor 5' dischargesslurry into tank 5 and thus transports slurry from tank 5 to tank 5';while the eductor 'i' returns slurry to tank 5.

In accordance with one embodiment of the present invention, a stream ofbarium sulphide liquor is introduced by an inlet pipe lil into the tank5. The barium sulphide liquor may, if desired, b-e introduced intoeither of the other tanks 5 and 5 or into any two or all of the tanks.The barium sulphide liquor on coming into contact with the zinc sulphatesolution reacts therewith to form a precipitate of crude normallithopone, which then circulates through the system of tanks togetherwith the slurry oi crude Zinc sulphide. Any reaction that may occurbetween the barium sulphide solution and the sulphuric acid liberated bythe reaction which is simultaneously proceeding, does not aifect thefinal result, since the reaction regenerates hydrogen sulphide gas whichthen reacts with the zinc sulphate solution to form zinc sulphideequivalent to the barium sulphate lformed by the reaction between thebarium sulphide and sulphuric acid. The amount of barium sulphideintroduced into the tank 5 is adjusted (by valve 52) with respect to theamount of zinc sulphate solution introduced so as to produce a highstrength lithopone of the desired zinc sulphide content.

In the production of Zinc sulphide by the method of U. S. Patent No.2,020,325 a preferred concentration of zinc sulphate solution is a ZnSOicontent equivalent to 30 grams Zn per liter. In the practice of thepresent invention, this concentration of the Zinc sulphate solution maybe increased to compensate for the zinc sulphate consumed by reactionwith the barium sulphide solution introduced.

In another embodiment of the invention, a slurry of crude lithopone insuspension in water is introduced into the system of tanks 5, 5 and 5through the inlet pipe Hl, and is permitted to circulate through thesystem together with the slurry of crude zinc sulphide being producedtherein by the reaction of hydrogen sulphide gas with Zinc sulphatesolution. The crude lithopone slurry may be introduced into any one ormore of the tanks 5, 5 and 5". The concentration of the zinc sulphatesolution introduced into the system through the pipe 2| rmay beincreased to compensate for the dilution eiiecteol by the water in theslurry of crude lithopone; or, the slurry of crude lithopone may be insuspension in an aqueous solution oi' zinc sulphate of equal strength tothat of the fresh zinc sulphate solution introduced into the system.

In another embodiment of the invention, crude lithopone in the form ofslurry is added to an aging tank 43 through an inlet pipe 44 having avalve 45. The aging tank has a peripheral overow launder l1 andassociated liquor outlet pipe ifi-8, and its conical bottom has anoutlet i5 with control valve 5l) for the discharge of the aged andthickened slurry. rThe crude slurry of lithopone thus introduced is agedwith the crude zinc sulphide slurry discharged through the pipe 38 fromthe last mixing tank 5". The two pipes :i3 and 38 may advantageouslydischarge into a distributing hood 35 at the top of the aging tank. Therelative amounts of the zinc sulphide slurry discharged through the pipe38 and returned to the tank 5 are controlled by appropriate adjustmentof the pinch valves 36 and te on the hose connections 35" and 39,respectively. This aging operation may for example be continued for fromfour to twelve hours when the crude zinc sulphide slurry is producedfrom zinc sulphate solution containing about grams Zn per liter so thatthe crude slurry after discharge from the tank 5 into the aging tank i3has a suiphuric acid content of about 4.5%.

During the aging of a crude zinc sulphide slurry produced by theinteraction of hydrogen sulphide gas and zinc sulphate solution, thereaction between hydrogen sulphide and zinc sulphate continues withfurther elimination of zinc sulphate from the solution and production ofzinc sulphide. This reaction appears to be due t'o the desorption ofadsorbed hydrogen sulphide from the zinc sulphide particles and itsreaction with the residual zinc sulphate in solution. In consequence ofthis aging reaction, the crude slurry of lithopone present during theaging is exposed to the action of a slurry, in which precipitation ofZinc sulphide by hydrogen sulphide gas is proceeding.

The crude pulp of high strength lithopone obtained in practicing theinvention as hereinbefore described is washed to remove acid. rI'hiswashing treatment is important since the precipitation of zinc sulphideby hydrogen sulphide gas results in the formation of sulphuric acidwhich must be removed from the crude precipitate prior to impartingthereto the usual slight degree of alkalinity. Thus, for example, thethickened slurry or pulp from the aging tank 43 is washed on a lter, thewashed filter cake is repulped and then end-pointed. The crude highstrength lithopone pulp is then subjected to the customary subsequentoperations of ltering, drying. calcining, quenching, wet disintegration,drying and drygrinding.

The finished high strength lithopone made in accordance with theinvention possesses entirely satisfactory pigmentary properties. Itstinting strength is substantially superior to that of a high strengthlithopone of the same zinc sulphide conm tent produced by mixing crudenormal lithopone With crude washed zinc sulphide prepared by thehydrogen sulphide process. Thus, for example, where crude lithopone isprecipitated in situ in the mixing system as hereinbefore described, aproduct containing 42.7% total zinc calculated as zinc sulphide has atinting strength equal to a high strength lithopone containing about 55%zinc sulphide produced by mixing crude lithopone with crude and washedZinc sulphide prepared by the hydrogen sulphide process.

I claim:

l.. The method of producing high strength lithopone which comprisesincluding coprecipated zinc sulphide and barium sulphate in a slurry,7in which precipitation of zinc sulphide by the reaction between hydrogensulphide and zinc sulphate is' proceeding and thereby subjecting thezinc sulphide in the coprecipitate to the same conditioning environmentas the zinc sulphide precipitated by hydrogen sulphide, and washing theresulting precipitate mixture to remove acid preparatory to thecustomary subsequent operations of lithopone manufacture.

2. The method of producing high strength lithopone which comprisesprecipitating zinc sulphide by the reaction between hydrogen sulphideand zinc sulphate in a slurry containing coprecipitated zinc sulphideand barium sulphate, washing the resulting precipitate mixture to removeacid, and subjecting the washed precipitate mixture to the customarysubsequent operations of lithopone manufacture.

3. The method of producing high strength lithopone which comprisescompleting with a detention period of several hours the precipitation ofzinc sulphide by the reaction between hydrogen sulphide and zincsulphate in a slurry containing coprecipitated zinc sulphide and bariumsulphate, and washing the resulting precipitate mixture to remove acidpreparatory to the customary subsequent operations of lithoponemanufacture.

4. The method of producing high strength lithopone which comprisesprecipitating Zinc sulphide by the reaction between hydrogen sulphideand zinc sulphate in a slurry containing coprecipitated zinc sulphideand barium sulphate, repeatedly mixing the slurry with hydrogen sulphidegas in a series of eductors through which the gas is entrained by theslurry, and washing the resulting precipitate mixture to remove acidpreparatory to the customary subsequent operations of lithoponemanufacture.

5. The method of producing high strength lithopone which comprisesprecipitating zinc sulphide by the reaction between hydrogen sulphideand zinc sulphate in a slurry containing coprecipitated zinc sulphideand barium sulphate, repeatedly mixing the slurry with a relatively muchlarger volume of hydrogen sulphide gas in an eductor discharging into anatmosphere of hydrogen sulphide gas in a closed tank partly lled withthe slurry, and washing the resulting precipitate mixture to remove acidpreparatory to the customary subsequent operations of lithoponemanufacture.

6. The method of producing high strength lithopone which comprisesprecipitating Zinc sulphide by the reaction between hydrogen sulphideand Zinc sulphate in a slurry containing coprecipitated zinc sulphideand barium sulphate, repeatedly mixing the slurry with hydrogen sulphidegas in a series of eductors through which the gas is entrained by theslurry, subjecting the finally mixed slurry to an aging treatment ofseveral hours duration to substantially complete the reaction betweenhydrogen sulphide and Zinc sulphate, and washing the resultingprecipitate mixture to remove acid preparatory to the customarysubsequent operations of lithopone manufacture.

7. The method of producing high strength lithopone which comprisesprecipitating zinc sulphide by the reaction between hydrogen sulphideand zinc sulphate in a slurry containing coprecipitated zinc sulphideVand barium sulphate, mixing the slurry with a relatively much largervolume of hydrogen sulphide gas in an eductor discharging into anatmosphere of hydrogen sulphide gas in a closed tank partly lled withthe slurry, subjecting the finally mixed slurry to an aging treatment ofseveral hours duration to substantially complete the reaction betweenhydrogen sulphide and Zinc sulphate, and Washing the resultingprecipitate mixture to remove acid preparatory to the customarysubsequent operations of lithopone manufacture.

8. The method of producing high strength lithopone which comprisesprecipitating zinc sulphide by the action of hydrogen sulphide upon anaqueous solution of Zinc sulphate in the presence of a oo-precipitate ofbarium sulphate and zinc sulphide formed in situ by introducing bariumsulphide liquor, completing the precipitating reactions in an agingtreatment of several hours duration, and washing the resultingprecipitate to remove acid preparatory to the customary subsequentoperations of lithopone manufacture.

9. The method of producing high strength lithopone which comprisesprecipitating zinc sulphide by the action of hydrogen sulphide upon anaqueous solution of zinc sulphate in the presence of a co-precipitate ofbarium sulphate and zinc sulphide formed in situ by introducing bariumsulphide liquor, repeatedly mixing with hydrogen sulphide gas the slurryresulting from the partial interaction of said precipitants in a seriesof eductors through which the gas is entrained by the slurry, andwashing the resulting precipitate to remove acid preparatory to thecustomary subsequent operations of lithopone manufacture.

l0. The method of producing high strength lithopone which comprisesprecipitating zinc sulphide by the action of hydrogen sulphide upon anaqueous solution of Zinc sulphate in the presence of a co-precipitate ofbarium sulphate and zinc sulphide formed in situ by introducing bariumsulphide liquor, repeatedly mixing a slurry resulting from the partialinteraction of said precipitants with a relatively much larger volume ofhydrogen sulphide gas in an eductor discharging into an atmosphere ofhydrogen sulphide gas in a closed tank partly iilled with the slurry,and washing the resulting precipitate to remove acid preparatory to thecustomary subsequent operations of lithopone manufacture.

11. The method of producing high strength lithopone which comprisesprecipitating zinc sulphide by the reaction between hydrogen sulphideand Zinc sulphate, repeatedly mixing the slurry resulting from thepartial interaction of the hydrogen sulphide and zinc sulphate withhydrogen sulphide gas in a series of eductors through which the gas isentrained by the slurry, incorporating coprecipitated Zinc sulphide andbarium sulphate in the finally mixed slurry of Zinc sulphide andsubjecting the resulting mixture to an aging treatment of several hoursdura' tion, and Washing the resulting precipitate mixture to remove acidpreparatory to the customary subsequent operations of lithoponemanufacture.

12. The method of producing high strength lithopone which comprisesintroducing separately co-procipitated zinc sulphide and barium sulphateinto a slurry in which precipitation of zinc sulphide by the reactionbetween hydrogen sulphide and zinc sulphate is proceeding and therebysubjecting the zinc sulphide in the co-precipitate to the sameconditioning environment as the Zinc sulphide precipitated by hydrogensulphide, and washing the resulting precipitate mixture to remove acidpreparatory to the customary subsequent operations of lithoponemanufacture.

LEON S. HOLSTEIN.

